Warn if the executable of the service being installed could be overwritten by other system users

Fixes #2579

Until this is handled by `kardianos/service`

dnscrypt-proxy/main.go

@@ -93,6 +93,9 @@ func main() {
 			dlog.Fatal(err)
 		}
 		if *svcFlag == "install" {
+			if fullexecpath, err := os.Executable(); err == nil {
+				WarnIfMaybeWritableByOtherUsers(fullexecpath)
+			}
 			dlog.Notice("Installed as a service. Use `-service start` to start")
 		} else if *svcFlag == "uninstall" {
 			dlog.Notice("Service uninstalled")